This application is related to, and claims priority from, Japanese Patent Application No. 2001-260082, filed on Aug. 29, 2001, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
The present invention generally relates to lubrication systems of outboard motors for watercraft. In particular, the present invention relates to an improved lubricant drain arrangement for a multi-cylinder internal combustion engine.
2. Description of the Related Art
Outboard motors containing internal combustion engines are commonly used for powering watercraft. A housing is mounted to a transom of the watercraft and typically encloses the engine. Rotation of a crankshaft of the internal combustion engine drives a driveshaft, which, in turn, drives a water propulsion device, such as a propeller. During normal operation of the watercraft, the propeller is submerged beneath a water surface. Rotation of the propeller moves the watercraft across the water surface.
Many internal combustion engines contained with an outboard motor include multiple cylinders and operate on a four-stroke combustion cycle. The four-stroke combustion cycle is well known to those of skill in the art and, therefore, will not be explained in detail herein. Four-stroke engines commonly comprise a crankcase in which the crankshaft is housed. Typically, in an outboard motor, the crankshaft assumes a generally vertical orientation. A cylinder block extends generally horizontally from the crankcase. The cylinder block defines multiple cylinder bores, each of which define a generally horizontal axis. A cylinder head member is affixed to the cylinder block to close the ends of the cylinder bores and, along with pistons, define combustion chambers of the internal combustion engine.
Internal combustion engines generally require lubricant for normal operation. Four-cycle engines typically employ a recirculating type of lubrication system. In such a system, a lubricant pump supplies lubricant to various moving components of the engine, including components within the crankcase chamber. Lubricant is evacuated from the crankcase chamber and returns to the lubricant reservoir, which is typically mounted below the crankcase chamber. Thus, drainage of the lubricant from the crankcase chamber to the lubricant reservoir is essential to ensure that a sufficient level of lubricant is made available to the lubricant pump for further distribution throughout the internal combustion engine.
An example of a typical lubricant drain arrangement is illustrated within the crankcase member shown in FIG. 1. The crankcase member illustrated in FIG. 1, along with additional details of an associated engine, may be found in Japanese Patent Application Publication No. JP-A-9-256904.
The crankcase member 10 illustrated in FIG. 1 is generally semi-cylindrical, or bowl-shaped, and defines an essentially hollow interior space. The crankcase member 10 is adapted to be connected to a cylinder block of an internal combustion engine at a peripheral mating surface 12 by a plurality of fasteners, such as bolts, which pass through a plurality of apertures 14 and thread into the cylinder block of the internal combustion engine. The crankcase member 10 and the cylinder block cooperate to define a crankcase chamber, which houses the crankshaft of the internal combustion engine.
The crankshaft is supported by a plurality of bearing surfaces 16 defined by upper and lower end walls of the crankcase member 10 and by one or more supports 18, which are intermediate to the upper and lower wall portions of the crankcase member 10 and divide the crankcase chamber into a plurality of sections. The supports 18 are generally provided to support the crankshaft and are located at a position between each cylinder bore. Accordingly, each section of the crankcase chamber is associated with an individual cylinder bore. The supports 18 also provide rigidity to the crankcase member 10 and thus absorb forces transmitted to the crankshaft due to combustion within the combustion chambers of the internal combustion engine.
A pair of lubricant drain passages 20 pass through the supports 18 and through a lower end of the crankcase member 10 to permit lubricant to drain from the crankcase chamber and, eventually, return to the lubricant reservoir. A thin-walled support, or rib 22, is provided along one side of the lubricant passage 20 within each section of the crankcase chamber. The ribs 22 act to restore lost strength and rigidity of the crankcase member 10 due to the formation of the lubricant passages 20 through the supports 18. The ribs 22 may also be arranged to guide lubricant, which is flung from the crankshaft, into the lubricant passage 20.
An aspect of the present invention is the discovery that, with the lubricant drain arrangement as illustrated in FIG. 1, lubricant may become trapped on a side of the rib 22 opposite the lubricant drain passage 20. Trapped lubricant tends to degrade due to elevated temperatures within the crankcase chamber and, once compromised, may not effectively lubricate the moving parts of the internal combustion engine. Additionally, trapped lubricant may enter the cylinder bore where it may pass by the piston rings and into the combustion chamber. Lubricant passing into the combustion chamber is then burned, and results in undesirable emissions from the engine. Accordingly, preferred embodiments of the present invention incorporate a lubricant drain passage that is recessed from an inner wall of the crankcase chamber. Such an arrangement preserves the strength of the components of the engine comprising the crankcase chamber and inhibits lubricant from becoming trapped within the crankcase chamber.
Another aspect of the present invention involves an outboard motor including an internal combustion engine and a propulsion device. A lubrication system is configured to deliver lubricant to a portion of the engine. The engine has a crankshaft arranged in a generally vertical manner and a driveshaft connects the crankshaft to the propulsion device. The engine includes a cylinder block and a crankcase. The cylinder block defines a plurality of cylinder bores, each cylinder bore defining a generally horizontal axis and being spaced from one another in a vertical direction. The cylinder block has a first wall generally aligned with the first end of the cylinder bores nearest the crankshaft. The cylinder skirt extends generally from a periphery of the first wall and terminates in the first mating surface. The crankcase includes a second wall, a second mating surface, and a peripheral wall extending between the second wall and the second mating surface. The cylinder blocks in the crankcase are assembled such that the first mating surface faces the second mating surface and the cylinder block and crankcase define a crankcase chamber therebetween. A plurality of support members extend from the first wall and the second wall in a paired configuration and terminate in cooperating bearing surfaces to rotatably support the crankshaft. A recess is defined by one of the cylinder block and the crankcase and extends beyond one of the first wall and the second wall, away from the crankcase chamber. An oil drain passage communicates with the recess and extends in a downward direction past the plurality of support members and through a lower end of one of the cylinder skirt and the peripheral wall.
A further aspect of the present invention involves an outboard motor including an internal combustion engine and a propulsion device. A lubrication system is configured to deliver lubricant to a portion of the engine. The engine has a crankshaft arranged in a generally vertical manner and a driveshaft connecting the crankshaft to the propulsion device. The engine includes a cylinder block and a crankcase. The cylinder block defines a plurality of cylinder bores, each cylinder bore defining a generally horizontal axis and being spaced from one another in a vertical direction. The cylinder block has a first wall generally aligned with a first end of the cylinder bores, nearest the crankshaft. A cylinder skirt extends generally from a periphery of the first wall and terminates in a first mating surface. The crankcase includes a second wall, a second mating surface and a peripheral wall extending between the second wall and the second mating surface. The cylinder block and the crankcase are assembled such that the first mating surface faces the second mating surface and a cylinder block in the crankcase define a crankcase chamber therebetween. A plurality of support members extend from the first wall and the second wall in a paired configuration and terminate in cooperating bearing surfaces to rotatably support the crankshaft. A plurality of apertures extend through the plurality of support members of the cylinder block and a lower end of the cylinder skirt. The apertures are aligned along a common axis and a plug closes the aperture of the cylinder skirt. An oil guide passage communicates with the lower-most of the cylinder bores and the aperture of the cylinder skirt. An oil drain passage communicates with the oil guide passage and extends through the cylinder block to permit lubricant to be evacuated from the crankcase chamber.
Yet another aspect of the present inventions involves an internal combustion engine. A lubrication system is configured to deliver lubricant to a portion of the engine. The engine has a crankshaft arranged in a generally vertical manner and includes an engine body defining a plurality of cylinder bores and a crankcase chamber. Each cylinder bore defines a generally horizontal axis and is spaced from one another in a vertical direction. The crankshaft chamber has a pair of opposing walls, one of the walls being between the crankshaft and the cylinder bores. A plurality of support members extend from the opposing walls in a pair to configuration and terminate and cooperating, bearing surfaces to rotatably support the crankshaft. A recess is defined by the engine body and extends beyond one of the opposing walls away from the crankshaft. The recess defines an oil drain passage extending in a downward direction to a lower end of the engine body.
Still a further aspect of the present invention involves an internal combustion engine. A lubrication system is configured to deliver lubricant to a portion of the engine. The engine has a crankshaft defining a generally vertical crankshaft axis and includes an engine body defining a plurality of cylinder bores and a crankcase chamber. Each cylinder bore defines a generally horizontal axis and are spaced from one another in a vertical direction. The crankshaft chamber has a pair of opposing walls, one of the walls being between the crankshaft and the cylinder bores. A plurality of support members extend from the opposing walls in a paired configuration and terminate in cooperating bearing surfaces to rotatably support the crankshaft. A plurality of apertures extend through the plurality of support members between the crankshaft and the cylinder bores and a lower end of the engine body. The apertures are aligned along a common axis and a plug closes the aperture of the engine body. An oil drain arrangement communicates with a lowermost of the cylinder bores and the aperture of the engine body. The oil drain arrangement extends through the engine body to permit lubricant to be evacuated from the crankcase chamber.